If you get off those meds I'm sure your pcp will suggest multivitamins to help reverse the hypothyroidism if it's a mild case. Generally multivitamins help reverse and prevent a lot of disorders such as anemia. Aps can cause weight gain, but so can hypothyroidism. You take such a small dose that I don't think it would affect weight gain, so my guess is your hypothyroidism could be causing weight gain.